Re: [PATCH 3/6] bio: add allocation cache abstraction

[adding Thomas for a cpu hotplug questions]

+static void bio_alloc_cache_destroy(struct bio_set *bs)
+{
+	int cpu;
+
+	if (!bs->cache)
+		return;
+
+	preempt_disable();
+	cpuhp_state_remove_instance_nocalls(CPUHP_BIO_DEAD, &bs->cpuhp_dead);
+	for_each_possible_cpu(cpu) {
+		struct bio_alloc_cache *cache;
+
+		cache = per_cpu_ptr(bs->cache, cpu);
+		bio_alloc_cache_prune(cache, -1U);
+	}
+	preempt_enable();

If I understand the cpu hotplug state machine we should not get any new
cpu down callbacks after cpuhp_state_remove_instance_nocalls returned,
so what do we need the preempt disable here for?

+	/*
+	 * Hot un-plug notifier for the per-cpu cache, if used
+	 */
+	struct hlist_node cpuhp_dead;

Nit, even if we don't need the cpu up notifaction the node actually
provides both.  So I'd reword the comment drop the _dead from the
member name.

Otherwise looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>